The subject matter disclosed herein relates generally to isotope production systems, and more particularly to isotope production systems having a target material that is irradiated with a particle beam.
Radioisotopes (also called radionuclides) have several applications in medical therapy, imaging, and research, as well as other applications that are not medically related. Systems that produce radioisotopes typically include a particle accelerator, such as a cyclotron, that accelerates a beam of charged particles (e.g., H− ions) and directs the beam into a target material to generate the isotopes. The cyclotron is a complex system that uses electrical and magnetic fields to accelerate and guide the charged particles along a predetermined orbit within an acceleration chamber. When the particles reach an outer portion of the orbit, the charged particles form a particle beam that is directed toward a target assembly that holds the target material for isotope production.
The target material, which is typically a liquid, gas, or solid, is contained within a chamber of the target assembly. The target assembly forms a beam passage that receives the particle beam and permits the particle beam to be incident on the target material in the chamber. To contain the target material within the chamber, the beam passage is separated from the chamber by one or more foils. For example, the chamber may be defined by a void within a target body. A target foil covers the void on one side and a section of the target assembly may cover the opposite side of the void to define the chamber therebetween. The particle beam passes through the target foil and deposits a relatively large amount of power within a relatively small volume of the target material, thereby causing a large amount of thermal energy to be generated within the chamber. A portion of this thermal energy is transferred to the target foil.
At least some known systems use two foils that are separated by a cooling chamber. A first foil separates the vacuum in the acceleration chamber of the cyclotron from the cooling chamber and a second foil (or target foil) separates the cooling chamber from the chamber where the target material is located. As described above, the second foil absorbs thermal energy from the chamber. The first foil may also generate thermal energy when the particle beam is incident on the first foil.
It is important to transfer the thermal energy away from the foils. In addition to the elevated temperatures, the foils may experience different pressures. The stress caused by the temperature and different pressures render the foils vulnerable to rupture, melting, or other damage. If the foils are damaged, the level of energy that enters the production chamber increases. Greater energy levels may generate unwanted isotopes or other impurities that render the target material unusable. Accordingly, the lifetime of a foil can be lengthened by reducing the thermal energy in the foil.
To address this challenge, conventional systems include a cooling system that transfers the thermal energy away from the first and second foils. The cooling system directs a cooling medium (e.g., helium) through the cooling chamber that absorbs thermal energy from the foils. This cooling system, however, can be complex, costly, and time-consuming to assemble and operate.